Various techniques are known for the regeneration or treatment of hydrodehalogenation or hydrodechlorination catalysts. The following are some examples of disclosures that deemed to be relevant to the present invention:
U.S. Pat. No. 4,980,324 to C. S. Kellner et al. discloses the regeneration and/or activation of a noble metal catalyst by the use of a fluorohalocarbon and/or a fluorohydrocarbon. In more recent U.S. Pat. No. 5,057,470, C. S. Kellner advocates the contacting of a hydrodehalgenation catalyst with an atmosphere comprising chlorine gas at elevated temperature for a time that is sufficient to improve the catalytic activity of the catalyst.
U.S. Pat. No. 4,374,047 of A. Bozon et al. teaches the pre-loading of a porous catalyst carrier with an aqueous solution of ammonium chloride prior to applying a coating containing platinum and/or palladium to the surface of the treated porous catalyst carrier.
More recent U.S. Pat. No. 5,105,032 to M. T. Holbrook et al. indicates that a supported platinum catalyst, which has been subjected to chloride pre-treatment, can be used in the hydrodechlorination of carbon tetrachloride to produce chloroform and methylene chloride. The types of chloride treatment that are disclosed by this patent include treatment of the catalyst with hydrochloric acid and chlorine at an elevated temperature.
The regeneration of a deactivated catalyst which is useful in the production of aromatic compounds, rather than as a hydrodechlorination catalyst, is described in European Patent Publication No. 535,619. In this patent, a deactivated catalyst containing a zeolite and a noble metal from Group VIII of the Periodic Table is treated with a variety of halogen and halogen-containing compounds including such species as hydrogen chloride, ammonium chloride, and ammonium fluoride.
In U.S. Pat. No. 5,721,189, a process for enhancing the durability of a supported nobel metal hydrodechlorination catalyst is taught which comprises treating the supported catalyst, which comprises support and catalytic nobel metal, with a non-elemental halide compound, which is not a mineral acid. A preferred halide compound for use in that invention is ammonium chloride.